It has heretofore been known a coated cutting tool having a substrate comprising a cemented carbide and a coating layer formed on the surface of the substrate. The coating layer comprises, for example, at least one kind of compound selected from the group consisting of a carbide, a nitride, a carbonitride, a carboxide and a carboxynitride of Ti. The coating layer may contain aluminum oxide. The coating layer may be a single layer or may contain two or more layers. The coating layer is formed on the surface of the substrate by the chemical vapor deposition method. A whole thickness of the coating layer is 3 to 20 μm. The coated cutting tool having such a coating layer is used for cutting processing of a steel, cast iron, etc.
In general, a tensile stress remains in the film formed on the surface of the tungsten carbide-based cemented carbide. When the tensile stress is remained in the film, fracture strength of the coated cutting tool is lowered and the coated cutting tool is easily fractured.
As a technique to release the tensile stress remained in the film, it has been known a technique in which cracks are generated at the film by shot peening (for example, see Patent Document 1).
It has been known a coated cutting tool comprising a substrate and a film formed onto the substrate, wherein the film contains a TiCN film having a tensile stress and an α type Al2O3 film having a compression stress, and the TiCN film is located between the substrate and the α type Al2O3 film (for example, see Patent Document 2).